Mechanisms of distal-nephron Li+ reabsorption during dietary K+ restriction in rats

The mechanism by which dietary K+ restriction induces distal-nephron Li+ re absorption was investigated by administration of bendroflumethiazide (BFTZ) or vehicle in conscious Wistar rats. Changes in fractional excretion of Li + following administration of amiloride (Delta FELi) were used as an index of distal tubular Li+ reabsorption. The results revealed an absence of dist al tubular Li+ reabsorption in K+-replete rats (Delta FELi = 3.6+/-2.4%), i n contrast to K+ restriction in which Delta FELi was 24.0+/-2.7%, The dista l tubular Li+ reabsorption in K+-depleted rats was significantly reduced by preadministration of BFTZ (Delta FELi = 9.2+/- 0.9%), The fractions of Li and Na+ reabsorbed in the amiloride-sensitive segment were different in K-replete rats (9+/-6 vs. 60+/-6%), but similar in K+-depleted rats (61+/-5 vs. 73+/-4%), BFTZ administration to K+-depleted rats resulted in a proport ional decrease in these fractions, suggesting competition between Na+ and L i+ for reabsorption in the distal-nephron segment during K+ depletion. Thes e results are compatible with the hypothesis that during K+ depletion the r eabsorption of Li+ in the distal-nephron segment is competitively inhibited by Na+. Copyright (C) 2000 S. Karger AG, Basel.